This invention relates to cookware for use in microwave ovens. In particular, the invention relates to cookware which causes browning of the exterior surfaces of the food prepared through use of microwave energy such that the food has the same or similar appearance as food prepared by conventional ovens or grills.
The browning cookware contemplated by this invention is an improvement over that described in U.S. patents to Levinson, U.S. Pat. Nos. 3,701,872 and 3,777,099, and to Tanonis, et al, U.S. Pat. No. 4,542,271.
The Levinson patents teach cookware articles for and methods of heating food in a microwave type oven. The Levinson cookware includes a body portion made of a microwave non-absorptive material, a bed of resistive particles which utilize microwave radiation to create heat, and a plurality of metal rods or other heat conducting portions embedded within the resistive particles to conduct the heat generated by the resistive particles when exposed to microwave radiation. The described combination is formed as a cookware pan and as a bottom shelf in a microwave oven chamber. The food is placed on the cookware or shelf and exposed to microwave radiation. The microwave absorptive material, which is described as a ferrite material, causes what is described as an arcing and sparking on exposure to the microwaves and generates heat. The plurality of rods are placed in a pattern within the body member and the bed of particles so as to provide a heating pattern for the food placed on the cookware. The heat generated by the microwave absorptive particles is conducted by the plurality of rods which are placed in proximity to the food. The heat in the rods causes browning of the food surfaces adjacent to the cookware or shelf.
The Tanonis et al patent describes a microwave absorptive material which is maintained within a polymer matrix. The matrix is cured onto the lower surface of the metallic pan which forms the cooking or browning surface. The matrix includes a combination of plastic type materials in which is embedded magnetite particles which absorb microwave energy. The magnetite creates heat by absorbing microwave energy and elevating in temperature to its Curie temperature. When the magnetite reaches this Curie temperature, the material stops absorbing microwave energy and remains at that temperature level. Magnetite does not heat by arcing and sparking as described in the Levinson patents. The magnetite material within the polymer matrix may be applied directly to the underside of the metallic pan of the cookware. The metallic pan is made from a thin sheet of aluminum or other high heat conducting material and is coated with a TEFLON (registered trademark for Tetra Fluoroethylene Fluorocarbon Polymer) or the like which acts as a non-stick cooking surface. The polymer and magnetite matrix is layered on the bottom of the metallic pan and is retained within the body of the microwave cookware.
The problem arising in known versions of microwave browning cookware is particularly exemplified by the method of cooking food outside of the microwave oven chamber. Typically, this type microwave cookware may be placed within the oven chamber and heated by exposure of the absorptive material to microwave radiation. The cookware is then removed from the oven chamber with the metal rods or pan retaining the heat generated by the absorptive material (ferrite or magnetite). The cookware is then utilized as a grilling surface to cook food by contact with the heated surfaces. The cookware may also be utilized in conjunction with the microwave energy by returning the heated cookware and the food into the oven chamber. In a typical situation the food, such as a sandwich, would be grilled on the heated surface of the cookware similar to heating on the surface of a griddle or frying pan. However, the amount of heat retained by the metal portions of the known cookware is insufficient to grill both sides of the food and to provide a browned or toasted surface on both sides. Typically, if the food and cookware is returned to the microwave oven, the microwave energy may cause some portions of the food (such as cheese in a sandwich) to be cooked faster than the surfaces being toasted or browned. Therefore, in known microwave cookware the amount of heat available to cook or grill the food is limited.
Another typical problem of known microwave cookware of this type relates to the deterioration of the coating on the cooking surface and also the metal materials when exposed to microwave radiation. Microwave browning wares, when utilized with any separate pan or dish, which is made of a metal material may cause a capacitance effect between the cooking surface and the separate pan. Such separate pans include those sold with frozen pies and the like which require cooking prior to consumption. If this article of food, which is sold in its own disposable cooking pan, were to be prepared in a microwave oven, the exterior food surfaces may not be properly browned since the microwave radiation would be reflected by the metal pan and the microwaves typically do not cause browning without a browning type ware. If the pan were placed on the browning ware, the space separating the cooking surface and the metalic pan would create the capacitance effect and would cause arcing through the coating. The arcs caused by the microwave energy also generally cause deterioration of the coating and the cooking pan. Additionally, use of cooking implements, such as spatulas, knifes or forks on the coated cookware, will cause the coating to be scratched or partially removed while cooking.